Deputy Prime Minister Nick Clegg hit out today at "distractions and falsehoods" being used by campaigners against a change in the electoral system.

He accused "paternalists and conservatives" of trying to create a "ludicrous caricature" of the Alternative Vote - saying they should "grow up".

But the Liberal Democrat leader again insisted that the coalition would not be torn apart by the increasingly acrimonious battle.

The intervention came amid signs that the pro-AV camp is losing ground ahead of the national poll on May 5.

Lib Dem Cabinet minister Chris Huhne warned earlier this week that the party's alliance with the Tories was being damaged by bitter sniping, saying the No campaign was indulging in "downright lies".

Speaking in London this morning, Mr Clegg said AV would help "clean up politics" by making MPs more accountable.

"But as with almost all changes that give people more power and more choice, paternalists and conservatives are lining up to try and block it," he said.

"The No campaign seems less interested in making the positive case for first past the post than attacking a ludicrous caricature of AV."

Mr Clegg said the arguments being used by opponents of the change were "distractions and falsehoods".

"First, the No campaign claims that AV will somehow help extremist parties like the BNP," he said.

"What astonishes me most about this claim is the brazen way it seeks to reverse the truth.

"AV will make it harder for extremist parties to get elected because it favours those who can appeal to a majority of voters in a seat.

"(BNP leader) Nick Griffin knows this, which is why he is campaigning for a No vote.

"You don't have to take my word for it, in the words of the BNP's deputy chairman Simon Darby: 'We are never going to get our feet under the table under the AV system'."

Mr Clegg dismissed the idea that AV would lead to more coalitions, saying Australia had experienced fewer hung parliaments than the UK.

And he also rejected allegations that the voting system would require new, expensive counting machines.

"This is simply untrue. There are no plans to bring in electronic machines. We won't need them. It won't happen," he said.

"This is the first time British people have ever had a choice on how to elect their MPs.

"They deserve a debate based on reason and reality, not prejudice and misinformation."

The deputy prime minister addressed head-on critics who have been using his own performance in government to attack AV.

"The truth is this: If we want a different kind of politics, one in which parties can work together in the national interest, we all have to grow up a bit. Compromise is not betrayal," he said.

Mr Clegg pointed out that his party was the junior coalition partner, and said the way for people to get more Lib Dem policies was to elect more of their MPs.

"In the meantime, I will continue to make what are sometimes difficult compromises, but ones which are always shaped as best I can by the Liberal values I hold dear," he added.

With polls suggesting the public may decide to keep first past the post on May 5, Mr Clegg stressed that the referendum was "only one part of a broader Liberal agenda of reform" being pushed through by the coalition.

He flatly denied speculation that defeat could fan disquiet among the Lib Dem rank-and-file - for whom electoral reform has long been a holy grail - and destroy his partnership with David Cameron.

Although action to tackle the UK deficit had "kept the wolves from the door" so far, they were "still lurking in the woods".

"If the coalition were to falter now the crisis we have worked so hard to avoid would threaten the nation again," Mr Clegg said.

"The work of this government will continue in the national interest regardless of the result of the referendum."

Mr Clegg cast himself as an "interloper" hoping to overthrow the Westminster status quo.

The Deputy Prime Minister has been stung by bitter personal attacks and was snubbed by Ed Miliband earlier this week when the Labour leader refused to share a platform with his Lib Dem counterpart.

Mr Clegg branded negative campaign tactics as a "really, really desperate attempt to try and fool the British people into thinking this referendum is about something else".

He said: "This is what happens when vested interests feel threatened. It really unsettles their cosy pattern of doing things.

"It's no wonder that when an interloper like me interrupts that, messes it up a bit, they get really, really aggressive because it messes up the nice, cosy way they have done things for ages."

He denied accusations that he was a liability to the Yes campaign, saying: "I don't think people are that daft.

"When people come to vote they will know the question before them is 'Do you maintain first-past-the-post with all its failings, a system that fostered the expenses scandal?' or 'Do you want something which keeps politicians on their toes?'.

"It's not a beauty contest between different politicians."

The Deputy Prime Minister, who previously described AV as "a baby step in the right direction", denied he would push for full proportional representation if the UK voted Yes on May 5.

He said: "We aren't going to enter into a Maoist, perpetual revolution .

"This is a once-in-a-blue-moon opportunity to change the electoral system. It's completely wrong to somehow suggest this is a stepping stone for something else.

"This is the change and it should be considered only on those merits."

And Mr Clegg shrugged off claims that a Yes result would lack legitimacy if it was supported by voters in Wales, Scotland and Northern Ireland, but rejected by the English electorate.

He said: "It's a national referendum and the result will be respected as a national outcome."

But shadow local government secretary Caroline Flint, who is launching the Labour No to AV campaign in Yorkshire, said: "For Nick Clegg to claim that AV will cure all our political ills is simply wrong. In fact, with his overblown claims he is in danger of damaging politics yet further.

"A vote for AV will lead to more hung parliaments, more ditching of manifesto promises and more broken promises. This is not what we want from our politicians.

"I'm a believer in strong and stable governments to deliver the best for everyone. That is why I am campaigning to protect one person, one vote."

There have been reports that the Lib Dem leadership is angry that the Prime Minister has reneged on a promise to maintain a low profile during the AV campaign.

While not mentioning Mr Clegg by name, a speech by Mr Cameron on Monday seemed to criticise his U-turn over tuition fee rises.

"I believe there should be real accountability between the pledges politicians put in their manifestos and the action they take in government. AV would damage that chain of accountability," the premier said.

In his address to the Ippr think-tank today Mr Clegg delivered a coded rebuke to Mr Cameron, decrying "dismal" attacks on "people working together for the national good".

"There are people on the left and the right who preach new politics and pluralism and yet are now so damning of its inevitable consequence, which is compromise," he said.

"You can't claim to stand for a new kind of politics, for a new kind of pluralism, and then vilify those who try to practice it."